\name{TclInterface}
\title{Low-level Tcl/Tk Interface}
%
\alias{.Tcl}
\alias{.Tcl.callback}
\alias{.Tcl.args}
\alias{$.tclvar}
\alias{$<-.tclvar}
\alias{tclvar}
\alias{.Tk.ID}
\alias{.Tk.newwin}
\alias{.Tk.subwin}
\alias{is.tkwin}
\alias{tkdestroy}
\alias{.TkWin}
\alias{.TkRoot}
\description{
  These functions and variables provide the basic glue between \R and the
  Tcl interpreter and Tk GUI toolkit. Tk
  windows may be represented via \R objects. Tcl variables can be accessed
  via the pseudo-list \code{tclvar}.
}
\usage{
.Tcl(...)
.Tcl.args(...)
.Tcl.callback(...)
.Tk.ID(win)
.Tk.newwin(ID)
.Tk.subwin(parent)
.TkWin
.TkRoot

tkdestroy(win)
is.tkwin(x)

tclvar$name
tclvar$name <- value
}
\arguments{
  \item{win}{a window structure}
  \item{x}{an object}
  \item{ID}{a window ID}
}
\details{
  Many of these functions are not intended for general use but are used
  internally by the commands that create and manipulate Tk widgets and
  Tcl objects.  At the lowest level \code{.Tcl} sends a command as a text
  string to the Tcl interpreter and returns the result as a text string.

  \code{.Tcl.args} converts an R argument list of \code{tag=value} pairs
  to the Tcl \code{-option value} style, thus
  enabling a simple translation between the two languages. To send a
  value with no preceding option flag to Tcl, just use an untagged
  argument. In the rare case one needs an option with no subsequent
  value \code{tag=NULL} can be used. Most values are just converted to
  character mode and inserted in the command string, but window objects
  are passed using their ID string, and functions are passed via the
  result of \code{.Tcl.callback}. Tags are converted to option flags
  simply by prepending a \code{-}

  \code{.Tcl.callback} converts \R functions to Tcl command strings.  The
  argument must be a function closure.  The
  return value is something of the form \code{\{ R_call 0x408b94d4 \}} in which
  the hexadecimal number is the memory address of the function.  
  \code{.Tcl.args} takes special precautions to ensure that the function
  will exist at that address by assigning the function into the relevant
  window environment (see below).

  Tk windows are represented as \R environments, all of which are
  enclosed in the \code{.TkWin} environment.  They contain initially just
  an \code{ID} variable identical to the Tk window name, a
  \code{parent} variable and a \code{num.subwin} variable (possibly
  inherited from \code{.TkWin}).  If the window obtains subwindows and
  callbacks, they are added as variables to the environment.
  \code{.TkRoot} is the top window with ID "."; this window is not
  displayed in order to avoid ill effects of closing it via window
  manager controls.  \code{.Tk.ID} extracts the \code{ID} of a window,
  \code{.Tk.newwin} creates a new window environment with a given ID and
  \code{.Tk.subwin} creates a new window which is a subwindow of a given
  parent window.

  \code{tkdestroy} destroys a window and also removes the reference to a
  window from its parent.

  \code{is.tkwin} can be used to test whether a given object is a window
  environment.

  \code{tclvar} is used to access Tcl variables. The Tcl variable name
  is used as if it were a list element name in \code{tclvar}, but in
  reality \code{tclvar} is an object of class \code{tclvar} and \code{$}
  and  \code{$<-} have special methods for that class.

}
\note{ Strings containing unbalanced braces are currently not handled
  well in many circumstances.
}
\seealso{\code{\link{TkWidgets}}, \code{\link{TkCommands},
    \code{\link{TkWidgetcmds}} 
}
\examples{
\dontrun{
## These cannot be run by example() but should be OK when pasted
## into an interactive R session with the tcltk package loaded
.Tcl("format \"\%s\\n\" \"Hello, World!\"")
f <- function()"HI!"
.Tcl.callback(f)
.Tcl.args(text="Push!", command=f) # NB: Different address

tclvar$xyzzy <- 7913 ; .Tcl("set xyzzy")
.Tcl("set xyzzy 3917") ; tclvar$xyzzy

top <- tktoplevel() # a Tk widget, see Tk-widgets
ls(envir=top, all=TRUE)
ls(envir=.TkRoot, all=TRUE)# .Tcl.args put a callback ref in here
}
}
\keyword{ misc }
